In the temperature range lying above approximately 800.degree. C., measurements of the temperature of objects in a remote, non-contact, manner or on moving parts (or both) is very difficult. The measurement of such high temperatures by a remote method is often carried out by so-called pyrometric techniques in which the effective "color" of the light emitted from the hot object to be measured is compared to that produced by an externally heated wire or other object whose temperature can be varied in a controlled manner and whose optical emission can be calibrated as a function of temperature. This method suffers from a number of shortcomings including errors which arise due to thermally induced changes in the emissivity of the object whose temperature is to be measured, background reflections or interference, and in some cases, to the deposition of partially transmitting films on windows which may be interposed between the pyrometer and the object. In the case of temperature measurements on moving parts, direct (i.e. non-remote) traditional temperature measurement techniques involving resistive thermometry or thermocouples require electrical contacts which necessitate the use of commutators. The attachment of such devices is not always practical or possible, and in any event, their use can introduce electrical noise and errors in the temperature determination. Additionally, thermocouples are subject to degradation and to calibration drift. The subject invention overcomes these problems by employing an inert "thermophosphor" whose fluorescence properties are temperature dependent but whose optical emission is independent of emissivity. Such a thermophosphor can be interrogated in a remote manner (i.e. without the use of direct electrical contacts) and can be interrogated on rapidly moving parts without the use of commutators.